This invention relates to a fuel injector for use in supplying fuel, under pressure, to the cylinders of an internal combustion engine.
A known fuel injector arrangement comprises a plunger reciprocable within a bore provided in a housing to pressurize fuel located within the bore. The bore communicates with a fuel pressure actuated injector such that once the fuel pressure within the bore exceeds a predetermined level, the injector opens and, thus, fuel injection commences.
In order to permit independent control of the injection pressure and the timing of injection, it is known to provide a spill valve which communicates with the bore, and an injection control valve which controls the pressure applied to a control chamber defined, in part, by a surface associated with a needle of the injector to control movement of the needle. In use, the spill valve remains open during initial inward movement of the plunger. Subsequently, the spill valve is closed, further inward movement of the plunger pressurizing the fuel within the bore. When injection is to commence, the injection control valve is actuated to connect the control chamber to a low pressure drain thus permitting movement of the needle away from its seating to commence fuel injection.
A known fuel injector of the aforementioned type includes a spill valve arrangement, which is controlled by means of a first actuator, and an injection control valve, which is controlled by means of a second actuator. A disadvantage of this type of injector is that, if the injection control valve fails to move from its lower seat, communication between the high pressure supply line and the control chamber cannot be broken and so fuel injection will not commence. The build up of high pressure fuel within the injector can cause damage to the components of the fuel injector, and to the fuel injector drive system.
It is an object of the invention to provide a fuel injector which alleviates this problem.
According to the present invention there is provided a fuel injector for use in an injector arrangement including a fuel pump having a pump chamber and a spill valve controlling communication between pump chamber and a low pressure reservoir, the injector including a valve needle which is engageable with a valve needle seating, a control chamber arranged such that the fuel pressure therein urges the valve needle towards the valve needle seating, a control valve controlling the fuel pressure within the control chamber and an actuator arrangement controlling the operation of the control valve, wherein, when the actuator is de-energised, the control valve permits communication between the control chamber and the low pressure reservoir.
Preferably, the control valve comprises a valve member which is engageable with first and second valve seatings to control communication between the pump chamber and the control chamber and between the control chamber and the low pressure reservoir respectively. The valve member is preferably resiliently biased into a position in which it engages the first valve seating, energisation of the actuator arrangement causing movement of the valve member away from the first valve seating to break communication between the control chamber and the low pressure reservoir.
Such an arrangement is advantageous in that, if the control valve fails and the valve member becomes stuck in a de-actuated position, the valve member engages the first valve seating and the control chamber communicates with the low pressure reservoir. In such circumstances, the fuel pressure will be able to lift the valve needle away from its seating, avoiding the generation of excessive pressures within the injector and reducing the risk of damage to the injector and the associated fuel injector drive mechanism.
The spill valve and the control valve may be actuated independently by a single electromagnetic actuator. This provides the advantage that fewer electrical connections to the fuel injector are required than where the valves are controlled by independent actuators.
The injector may include a first housing part provided with a bore within which the control valve member is reciprocable, the first valve seating being defined by the bore. The second valve seating may be defined by an end surface of a second housing part in abutment with the first housing part.
Alternatively, both the first and second valve seatings may be defined by end surfaces of first and second housing parts.